My primary research objective is to describe the sequence of metabolic reactions which lead to the secretion of hydrochloric acid by the gastric mucosa and to identify those reactions which serve as the major controlling steps in this process. My approach to this problem relies heavily on the use of non-destructive optical techniques which permit the monitoring of certain intracellular reactions in the intact tissue. These techniques are used in conjunction with more conventional measurements of respiration and metabolic intermediates to characterize the time relations between various reactions as a means of identifying the controlling steps in acid secretion. Measurements of oxidative metabolism, intracellular pH, cyclic AMP and cellular morphology are related to acid secretion to provide a working model for the cellular control of acid production.